1. Field of the Invention
The present invention relates to an apparatus for generating a write pulse for an optical storage medium, and more particularly, to an apparatus for generating a digital write pulse using a ring oscillator.
This patent application is based on Korean Patent Application No. 2002-5214, the contents of which is incorporated herein by reference.
2. Description of the Related Art
There are various kinds of related art optical storage media, such as a 4.7 GB DVD-RAM, a 2.7 GB DVD-RAM, a DVD-RW, a DVD-R, and a CD-R. Write pulses are recorded on different parts of an optical storage medium depending on the type of optical storage medium, and can be represented by a resolution of, for example, one fortieth, one thirty fourth, or one thirtieth of a channel clock. Channel clock frequencies, which affect write pulses, may vary depending on the optical storage medium and its recording or reproducing speed. In general, an optical storage medium has a channel clock frequency of 4–120 MHz.
FIG. 1 is a block diagram of a related art apparatus for generating a write pulse for an optical storage medium, including a phase locked loop (PLL) circuit 100, a first selection block 110, a second selection block 120, and a write pulse generation block 130. The PLL circuit 100 converts a channel clock input CLK into N subclocks having a predetermined phase difference. The PLL circuit 100 may be embodied in an analog or digital manner, or may be replaced by a delay locked loop (DLL) circuit.
The first selection block 110 and the second selection block 120 each select one of the N subclocks output from the PLL circuits 100. At this time, the first selection block 110 is controlled so that it can select a value TSP indicating a start point of a pulse, and the second selection block 120 is controlled so that it can select a value TEP indicating an end point of the pulse. The write pulse generation block 130 generates a write pulse having a start point and an end point determined based on pulses, generated by the first and second selection blocks 110 and 120.
The aforementioned related art has various problems and disadvantages. For example, but not by way of limitation, although the related art apparatus for generating a write pulse for an optical storage medium has such a simple structure, it is necessary to increase the number of subclocks generated by the PLL circuit 100 to satisfy the high operational frequency bandwidth of an optical storage medium and enhance the resolution of a write pulse. As a result, great effort and time are required to develop a PLL circuit having a high resolution. When the related art PLL circuit adopts an analog manner, an interface circuit used for the PLL circuit to interface with digital equipment is also needed.
Accordingly, it is necessary to develop an apparatus for generating a write pulse for a digital optical storage medium, which requires less time and effort to develop and has a simple structure that can replace a PLL circuit when the PLL circuit malfunctions.